NMR and Mössbauer study of spin dynamics and electronic structure of ${\mathrm{Fe}}_{2+x}{\mathrm{V}}_{1-x}\mathrm{Al}$ and ${\mathrm{Fe}}_2\mathrm{VGa}$

In order to assess the magnetic ordering process in ${\mathrm{Fe}}_2\mathrm{VAl}$ and the related material ${\mathrm{Fe}}_2\mathrm{VGa},$ we have carried out nuclear magnetic resonance (NMR) and Mössbauer studies. ${}^{27}\mathrm{Al}$ NMR relaxation measurements covered the temperature range 4–500 K in ${\mathrm{Fe}}_{2+x}{\mathrm{V}}_{1-x}\mathrm{Al}$ samples. We found a peak in the NMR spin-lattice relaxation rate, ${}^{27}{(T}_1^{-1}),$ corresponding to the magnetic transitions in each of these samples. These peaks appear at 125 K, 17 K, and 165 K for $x=0.10,$ 0, and -0.05, respectively, and we connect these features with critical slowing down of the localized antisite defects. Mössbauer measurements for ${\mathrm{Fe}}_2\mathrm{VAl}$ and ${\mathrm{Fe}}_2\mathrm{VGa}$ showed lines with no hyperfine splitting, and isomer shifts nearly identical to those of the corresponding sites in ${\mathrm{Fe}}_3\mathrm{Al}$ and ${\mathrm{Fe}}_3\mathrm{Ga},$ respectively. We show that a model in which local band filling leads to magnetic regions in the samples, in addition to the localized antisite defects, can account for the observed magnetic ordering behavior.